1. Field of the Invention
This invention relates to a method of recording data on a magneto-optical recording medium and an apparatus therefor.
2. Description of the Related Art
Nowadays, a magneto-optical recording medium is available for use as an information recording medium permitting a high density of overwriting. In particular, a magneto-optical recording medium using a recording layer made from an amorphous alloy of a rare-earth metal with a transition metal possesses excellent characteristics.
A process of recording a data on such a magneto-optical recording medium will be briefly described below. A laser light is converged onto the surface of the magneto-optical recording medium in a shape of a small spot having approximately a size of the wavelength thereof to increase the temperature in a recording layer to about 150 to 200.degree. C. When the temperature in the recording layer of the magneto-optical recording medium heated with a laser light becomes above the Curie temperature Tc, a magnetization phenomenon disappears at the corresponding portion in the magneto-optical recording medium. At this time, if a direct-current bias magnetic field is applied to the magneto-optical recording medium in a unitary direction by means of a magnet, then a magnetization inversion arises to emerge a mark or pit when the heated portion of the recording layer returns to room temperature.
An example of an apparatus for recording data on a magneto-optical recording medium in this manner is disclosed in the Japanese Laid-open Patent Gazette No. Heisei 1-292603. The recording apparatus in the Japanese patent has a circuit configuration as shown in FIG. 1. In FIG. 1, a channel clock generator 9 generates a channel clock signal CHCK, as shown in FIG. 2, on the basis of an information pre-formatted on a magneto-optical disc 8. A laser driver 11 allows a laser diode 1 to make a pulse emission in accordance with the channel clock signal CHCK, thereby irradiating a laser pulse beam LPB, as shown in FIG. 2, onto the magneto-optical disc 8 in a spot shape by means of an objective lens 3. A data signal generator 6 generates a modulated magnetic field MM, as shown in FIG. 2, using a magnetic head 5 installed in the vicinity of the magneto-optical disc 8. Accordingly, a recording mark train RMT, as shown in FIG. 2, corresponding to a channel bit train CHBT as shown in FIG. 2 emerges at the magneto-optical disc 8. Since a laser light is irradiated onto the magneto-optical disc 8 in the pulse shape as described above, the recording marks emerging at the magneto-optical disc 8 are partially overlapped. Also, since the recording marks are overlapped, data recording density in the magneto-optical disc 8 increases.
Light power must be constantly maintained so as to produce recording marks of the same size. The light power determining the size of the recording marks may be strengthened or weakened depending on temperature, exterior interference, etc. Actually, the recording marks increase or decrease in size as recorded on the second track, shown in FIG. 3, depending on variation in light power. In detail, if the light power is appropriately maintained, each of the recording marks is of an appropriate size as recorded in a second track region SMTR. When light power is weakened, no problems are created because the size of the recording mark decreases as recorded in first track region FMTR. On the other hand, when light power is strengthened, the size of the recording mark increases as recorded in the third track region TMTR and the width of track is broadened to thereby cause a so-called "cross-erasing" that causes marks pre-recorded on the adjacent tracks to be erased. Such a variation in the light power can not heighten a track density in the magneto-optical recording medium above a certain limit.